Parsing wiring - about sensor and PLC - programmable logic

PLC digital input interface is not complicated, in order to improve the anti-jamming ability of PLC, the input interface adopts photoelectric coupler to isolate the transmission and internal processing circuit of the input signal. Therefore, at the input signal is conducting internal LED photoelectric coupler, the photoelectric coupler photocell receiving, can make reliable external input signal transmission.

at present PLC digital input ports of single side concurrent input and double end, because there's a difference, the user on a sensor matching external connection requires certain distinction and understanding to the correct use of sensors and programming of PLC for later work to lay a good foundation and system stability.

1, the classification of input type

the digital quantity input terminal of PLC, according to the dc and ac power points, according to the input interface classification by the single-ended concurrent input and double side input, single and total points to connect power are extremely SINK ( Sink Current, Current) , single and total points to connect power negative extremely SRCE ( The source Current irrigation Current) 。

2, words, an overview of the

SINK type for the current leakage from the input flow, it can be input connected to the power supply cathode, how interfaces within the photoelectric coupler is single and concurrent is positive, can answer the NPN sensors. SOURCE for current from the input stream into the SOURCE type, it can be input connected to the positive, how interfaces within the photoelectric coupler for single and total points for negative power, can answer the PNP sensor.

proximity switch and photoelectric switch three or four line output NPN and PNP output, when there is no signal for NPN proximity switch and photoelectric switch output of high level ( For internal pull-up resistor) , when there is a detection signal, internal NPN transistors conduction, switch output for the low level. When there is no signal for PNP proximity switch and photoelectric switch output for the low level ( For internal have a pulldown resistor) , when there is a detection signal, internal PNP transistors conduction, switch output for the high level.

only on the condition of the above, the sensor is normally open state.

3, according to the power supply configuration type

1) Dc input circuit

dc input circuit requirement for external input signal components of dc active passive dry contact or non-contact switch contact, when the external input element and positive conduction, the current through R1, internal LED photoelectric coupler, VD1 ( Interface instructions) To the COM port to form circuit, photoelectric coupler internal receiving tube accept external components conduction of signals, transfer to the internal processing; A way of interface provided by the dc power supply, dc input circuit;

dc can be provided by the PLC internal can also external dc power provided to the external input signal components. R2 in the circuit is the current bypass internal LED photoelectric coupler, guarantee the photoelectric coupler LED not by two wire close to switch, the static leakage current conduction.

( 2) Ac input circuit

ac input circuit requirement for external input signal component of passive dry contact or communication active non-contact switch contact, it has to do with the distinction between dc interface in front of the photoelectric coupler with level step-down circuit and bridge rectifier circuit. External components after connected with alternating current (ac), and current through R1, C2 after the bridge rectifier, become a step-down dc, after the follow-up circuit principle and the agreement of the dc.

communication is mainly PLC controller relative conditions, the wiring was provided little changed, etc; Such as proximity switch with two line communication directly replace the original travel switch.

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